# Merkle Tree

> Position in the stack: Sits inside the Shielding Layer and interacts directly with the Smart Contract Infrastructure.

#### <mark style="color:yellow;">**Purpose**</mark>

* **Efficient membership proofs** – Users prove a note exists in the shielded set without revealing which note it is.
* **Compact state** – A single 32‑byte Merkle root represents millions of shielded notes, keeping onchain storage minimal.
* **Incremental privacy** – Every new deposit grows the anonymity set, the Merkle root captures that growth in one hash.

#### <mark style="color:yellow;">**How It Works in Veilon**</mark>

1. **Deposit → Commitment**
   * When you shield assets, Veilon creates a *note commitment* (a hash of value + owner + randomness).
2. **Commitment → Merkle Leaf**
   * The commitment becomes a leaf in Veilon’s incremental Merkle tree stored onchain.
3. **Tree → Root**
   * After the leaf is inserted, smart contracts update the Merkle root. This root is the only piece the zk‑SNARK circuit needs.
4. **Spend → zk Proof**
   * To spend privately, you submit a zk proof that:
     * Knows a path from your leaf to the current root (membership).
     * Has a nullifier so the same note can’t be spent twice.
     * Reveals nothing about which leaf you used.

```javascript
function verifyMerkleProof(
  bytes32 leaf,
  bytes32[] memory proof,
  uint256 index
) public view returns (bool) {
  bytes32 hash = leaf;
  for (uint256 i = 0; i < proof.length; i++) {
    if ((index >> i) & 1 == 1) {
      hash = keccak256(abi.encodePacked(proof[i], hash));
    } else {
      hash = keccak256(abi.encodePacked(hash, proof[i]));
    }
  }
  return hash == currentMerkleRoot;
}
```


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